Questions before I Upgrade my Rig?

I was looking to Upgrade a tad what I'm using at the moment so I can increase what I can do on terms of gaming...but also look to support a 2nd Monitor I plan on getting.

Currently I have a I7 960 @ 3.2 Ghz

6 Gb Ram

a Gtx 560 Ti

Liquid cooling + about 6-7 fans ( forgot how many specifically.. )

and my power supply is 700W.

My plan was to grab a 2nd monitor, and go SLI with a 2nd 560 Ti and upgrade my power supply to about a 850 or so.

My questions is few but basically; I'm a bit new too SLI and was wondering.

A.) Should a 850W Power Supply be sufficient for 560's?

B.) Is the amount of cooling In my Pc seem adequate for two cards? ( was contemplating a external cooling to add to the back.. )

C.) Does it matter if the 2nd 560 is a OC version or do they have to be uniform in every way ( the 560 I got is standard, So it's only OC when I do it manually )